(a) Technical Field
The present invention relates to an electrolyte membrane for a fuel cell. More particularly, it relates to a hydrocarbon composite electrolyte membrane for a fuel cell, which is formed of an inexpensive hydrocarbon electrolyte membrane to ensure mechanical and thermochemical stability.
(b) Background Art
A fuel cell is an electricity generation system that converts chemical energy directly into electrical energy in a fuel cell stack. A fuel cell can be used as an electric power supply for small-sized electrical and electronic devices. For example, a fuel cell may be used for portable devices, industrial and household appliances, and automobiles.
One of the most attractive fuel cells for use in a vehicle is a proton exchange membrane fuel cell or a polymer electrolyte membrane fuel cell (PEMFC), which has the highest power density among the various types of fuel cells. The PEMFC has a fast start-up time and a fast reaction time for power conversion due to its low operation temperature.
The PEMFC comprises a fuel cell stack that includes a membrane-electrode assembly (MEA), a gas diffusion layer (GDL), a gasket and a sealing member, and a bipolar plate. The MEA in which an electrolyte/catalyst layer where an electrochemical reaction takes place is disposed on each side of a polymer electrolyte membrane through which hydrogen ions are transported. The GDL functions to uniformly diffuse reactant gases and transmit generated electricity. The gasket and a sealing member function to provide an appropriate airtightness to reactant gases and coolant, as well as to provide an appropriate bonding pressure. The bipolar plate functions to transmit reactant gases and coolant.
When the fuel cell stack is assembled using a plurality of unit cells, a combination of the MEA and the GDL is positioned in the center of each unit cell of the fuel cell stack. The MEA includes a cathode and an anode as the electrode/catalyst layer, which is where an electrochemical reaction between hydrogen and oxygen takes place, disposed on both sides of the polymer electrolyte membrane. Moreover, the GDL and the gasket are sequentially stacked on both sides of the MEA, where the cathode and the anode are located.
The bipolar plate includes flow fields, through which the reactant gases (such as hydrogen as a fuel and oxygen or air as an oxidant) and coolant passes, and is disposed on the outside of the GDL.
After the plurality of unit cells are stacked together, an end plate for supporting a current collector, an insulating plate, and the stacked cells are connected to the outermost end, and the unit cells are repeatedly stacked between the end plates, thus forming the fuel cell stack.
A fuel cell vehicle equipped with a fuel cell stack is advantageous in that it is an environmentally-friendly vehicle that emits no exhaust gas; however, it suffers from a disadvantage in that it is difficult to commercialize due to high manufacturing costs.
As mentioned above, the MEA is a key component of the fuel cell and generally includes electrodes (such as the cathode and the anode) and an electrolyte. In the conventional art, fluorine electrolyte membranes (e.g., perfluorosulfonic acid) are being used; however, such membranes suffer from the disadvantage that they are very expensive.
Therefore, hydrocarbon electrolyte membranes (such as, e.g., sulfonated poly(phenylene)s, poly(ether ether ketone)s, and the like) have been extensively studied in an effort to develop inexpensive electrolyte membranes.
As shown in FIG. 1A, a conventional art hydrocarbon electrolyte membrane repeatedly contracts and expands during fuel cell operation as a result of water loss and water gain, respectively. Disadvantageously, these repeated cycles of contraction and expansion may result in the hydrocarbon electrolyte membrane being mechanically damaged due to significant dimensional changes caused by water gain and loss.
Moreover, when the MEA is made by a decal method, the electrodes and the electrolyte membrane are heated during a hot press process, and as a result the electrolyte contracts as shown in FIG. 1B. This is another example of a disadvantage of a conventional art hydrocarbon electrolyte membrane as the membrane may be mechanically damaged due to low thermal resistance.
In view of the foregoing, it is clear that conventional art hydrocarbon electrolyte membranes are not well suited to be used as the MEA of a fuel cell due to low mechanical stability and thermochemical durability.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention.